1. Field of the Invention
The invention relates to a control device for a motor vehicle, more particularly to a control device that employs a magnetic sensor to control direction and speed of a motor vehicle.
2. Description of the Related Art
An electric motor vehicle usually has a control device mounted proximate to a handle thereof for controlling its moving direction and speed. As shown in FIGS. 1 and 2, the control device 2 is mounted on a rear side of the handle 11 of the motor vehicle, and is coupled to a control rod 12.
The known control device 2, which has an operating principle based on that of a potentiometer, includes a case body 21 fixed to the handle 11 via an L-shaped bracket 111, a circuit board 22 mounted horizontally in the case body 21 and formed with a pair of arc-shaped resistive traces 221, and a slider assembly formed from a pivot axle 23 that is mounted rotatably on the case body 21, a contact carrier 24 that is disposed in the case body 21 and that is coupled co-rotatably to the pivot axle 23, and a pair of contact members 25 that are mounted on the contact carrier 24 for sliding along the resistive traces 221. A torsion spring 26 biases the pivot axle 23 to an initial position. A cover 27 is provided to close a top open side of the case body 21.
One end of the pivot axle 23 extends downwardly through the case body 21, and is coupled to the control rod 12. As such, the control rod 12 is operable to rotate the pivot axle 23 by a desired angle in a selected one of advancing and reversing directions.
When no external force is exerted on the pivot axle 23, the pivot axle 23 is disposed at the initial position due to the biasing action of the torsion spring 26. The contact members 25 are disposed at middle portions of the resistive traces 221 at this time.
Thereafter, when it is desired to move the motor vehicle in one of an advancing direction and a reversing direction, the control rod 12 is operated to rotate the pivot axle 23 in a corresponding one of a clockwise direction and a counterclockwise direction. As a result, the contact members 25 are displaced along the resistive traces 221. Since the operating principle of the control device 2 is based on that of a potentiometer, displacement of the contact members 25 along the resistive traces 221 will result in a control output having a voltage magnitude corresponding to movement of the control device 2 in the desired direction. That is, the larger the angle of rotation of the pivot axle 23, the faster will be the moving speed of the motor vehicle in the desired direction.
While the aforementioned conventional control device 2 can achieve its intended purpose, the following drawbacks are encountered during use:
1. The resistive traces 221 are likely to wear out due to friction contact with the contact members 25. As such, the service life of the control device 2 is relatively short.
2. The legs of the torsion spring 26 are likely to break due to stress after a period of use, thereby resulting in the inability to restore the pivot axle to the initial position. Hence, an unintended control output for driving movement of the motor vehicle is likely to be generated, which is hazardous.
Therefore, the object of the present invention is to provide a direction and speed control device that can overcome the aforesaid drawbacks associated with the prior art.
Accordingly, the present invention provides a direction and speed control device that comprises a casing, a sensing unit, and a magnet assembly. The casing is adapted to be mounted fixedly on a motor vehicle. The sensing unit is mounted in the casing, and includes a magnetic sensor. The magnet assembly includes a pivot axle, and first and second magnets. The pivot axle is mounted rotatably on the casing, and has a magnet carrying portion extending into the casing, and a driven portion extending from the magnet carrying portion and disposed outwardly of the casing. The first and second magnets are mounted on the magnet carrying portion of the pivot axle, and are disposed on opposite sides of the magnetic sensor. The driven portion of the pivot axle is operable externally of the casing for driving rotation of the pivot axle relative to the casing so as to move one of the first and second magnets toward the magnetic sensor and so as to move the other one of the first and second magnets away from the magnetic sensor. The sensing unit is adapted to generate a control output for controlling movement of the motor vehicle in one of an advancing direction and a reversing direction and for controlling moving speed of the motor vehicle in said one of the advancing and reversing directions in accordance with displacement of the first and second magnets relative to the magnetic sensor.